from https://dotat.at/@/2016-01-02-hammerspoon-hooks-for-better-screen-lock-security-on-mac-os-x.html

gemini-authored.lua

-- Define a logger for debugging (optional)
local log = hs.logger.new("caffeinate-watcher", "info")

-- Create the function that will be called when a power event happens
local function handleCaffeinateEvent(event)
    -- Get the string name of the event for logging
    local eventName = hs.caffeinate.watcher[event]
    log.f("Got caffeinate event: %s (id: %d)", eventName, event)

    if event == hs.caffeinate.watcher.screensDidLock then
        -- Code to run when the screen is locked
        hs.alert.show("Screen Locked!")
        -- Example: Execute a shell command/script
        -- hs.execute("${HOME}/.lock_script.sh")
    elseif event == hs.caffeinate.watcher.screensDidUnlock then
        -- Code to run when the screen is unlocked
        hs.alert.show("Screen Unlocked!")
        -- Example: Execute a shell command/script
        -- hs.execute("${HOME}/.unlock_script.sh")
    else
        -- Ignore other events like system sleep, screensaver, etc.
        log.f("Ignored event: %s", eventName)
    end
end

-- Create the watcher object and start it
local caffeinateWatcher = hs.caffeinate.watcher.new(handleCaffeinateEvent)
caffeinateWatcher:start()

log.i("Caffeinate watcher started.")

hammerspoon.script.lua

    -- hammerspoon script
    -- run key security scripts when the screen is locked and unlocked

    -- NOTE this requires a patched Hammerspoon for the
    -- session, screen saver, and screen lock hooks.

    local pow = hs.caffeinate.watcher

    local log = hs.logger.new("ssh-lock")

    local function ok2str(ok)
        if ok then return "ok" else return "fail" end
    end

    local function on_pow(event)
        local name = "?"
        for key,val in pairs(pow) do
            if event == val then name = key end
        end
        log.f("caffeinate event %d => %s", event, name)
        if event == pow.screensDidWake
        or event == pow.sessionDidBecomeActive
        or event == pow.screensaverDidStop
        then
            log.i("awake!")
            local ok, st, n = os.execute("${HOME}/bin/unlock_keys")
            log.f("unlock_keys => %s %s %d", ok2str(ok), st, n)
            return
        end
        if event == pow.screensDidSleep
        or event == pow.systemWillSleep
        or event == pow.systemWillPowerOff
        or event == pow.sessionDidResignActive
        or event == pow.screensDidLock
        then
            log.i("sleeping...")
            local ok, st, n = os.execute("${HOME}/bin/lock_keys")
            log.f("lock_keys => %s %s %d", ok2str(ok), st, n)
            return
        end
    end

    pow.new(on_pow):start()

    log.i("started")